1. Field of the Invention
The present invention relates to printing methods, printing apparatuses, and printing systems.
2. Description of the Related Art
Inkjet printers (hereinafter referred to simply as “printers”) that eject ink onto a medium such as paper to form dots are known as printing apparatuses for printing images. These printers repeat in alternation a dot forming operation of forming dots on a paper by ejecting ink from a plurality of nozzles, which move in the movement direction of a carriage, and a carrying operation of carrying, using a carrying unit, the paper in an intersecting direction (hereinafter, also referred to as the “carrying direction”) that intersects the movement direction. By doing this, a plurality of raster lines made of a plurality of dots in the movement direction are formed in the intersecting direction, thereby printing an image.
With this type of printer, there are discrepancies in the ink droplet ejection characteristics, such as the quantity of the ink droplet and the travel direction, among the nozzles. Discrepancies in the ejection characteristics are a cause of darkness nonuniformities in printed images, and thus are not preferable. Accordingly, a conventional method involves setting a correction value for each nozzle and adjusting the quantity of ink based on those correction values that are set. (See, for example, JP H06-166247A (pg. 4, 7, and 8).)
With this conventional method, first, correction patterns are printed on the paper. Printing of these correction patterns is performed by moving a head, which is provided with the nozzles, in a scanning direction while intermittently ejecting ink from all of the nozzles. Then, the darkness of the correction patterns that are printed is measured for each pixel. This darkness measurement is performed in the carrying direction for one spot in the scanning direction of the correction patterns.
However, with this conventional method, there is a possibility that the darkness that is obtained will change depending on the measurement position, even when measuring the same pixel. This is due to the fact that the dots that are formed are circular. In other words, with this type of printer, the dots that land on the paper spread out in a circular manner. The darkness thus differs between a case where the darkness is measured along a straight line that passes over the center of the dot and a case where the darkness is measured along a straight line that passes over the edge of the dot. That is, the darkness of the latter will be lower than the darkness of the former. Therefore, it is difficult to obtain an accurate darkness by measuring only one spot in the main-scanning direction.
Further, with this method there is also a possibility that the quality of the printed image will drop if interlacing is adopted as the print mode. Interlacing is a print mode in which a raster line that is not formed is set between raster lines that are formed in a single dot forming operation, and through a plurality of dot forming operations all of the raster lines are formed in a complementary manner, and with this print mode, adjacent raster lines are not printed by the same nozzle. Also, with interlacing, the nozzle that forms an adjacent raster line will not always be the adjacent nozzle. That is to say, it is possible for the combination of nozzles that form adjacent raster lines in the printed image to be different from the combination in the correction patterns. Here, darkness nonuniformities caused by bending in the flight path of the ink occur due to the spacing between adjacent raster lines becoming small or large, and also occur due to the combination of the nozzles forming the adjacent raster lines. Therefore, it is difficult to correct darkness nonuniformities that result from the combination of raster lines and nozzles using a correction pattern that is printed by ejecting ink from all of the nozzles.